THE HISTORY AND MAKE-UP OF OUR ATMOSPHERE
Air has been understood to be more than a single gas since Aristotle. However the exact nature and composition of air is fairly recent in terms mans knowledge and understanding.
Many people carried out research and investigations on air, perhaps unfairly only a few are listed below because they have been accredited with some discovery or another. From the mid 1700's though to the early 1800's, most of the constituent gases contained within air had been investigated by only a handful of people. These included..
- Joseph Black (1728-1799)
- Henry Cavendish (1731-1810)
- Joseph Priestly (1733-1804)
- Karl Wilhelm Scheele (1742-1786)
- Antione Laurent Lavosier (1743-1794)
- Daniel Rutherford (1749-1819)
- Lord John W.S. Rayleigh (1842-1919).
- Sir William Ramsey (1852-1916)
- Morris.W. Travers (1872-1961)
The approximate dates of discovery were as follows..
- Nitrogen was discovered by Rutherford in 1772.
- Oxygen was discovered separately by Priestley and Scheele in 1774 but it was considered to be a de-phlostigon because it wouldn't burn in its own right. During the latter part of the 1700's a couple called Marie Anne and Antione Lavosier experimented with air to try and establish the properties of Phlogiston, the 'element' contained within air that caused combustion. It was widely assumed within academic circles that this flammable gas burned and caused all other substances around it to be consumed in its flames. Therefore it seemed reasonable during this period, that if Phlogiston could be extracted from air, nothing else would burn. They showed that Phlogiston was a myth and deduced that a new element must be contained in air that supported combustion. They further deduced that it didn't burn in its own right and named the gas Oxygen.
- Carbon Dioxide was identified in 1756 by Black, a Scottish chemist. However, Lavoisier proved that this gas was an oxide of carbon and gave the gas its name.
- Hydrogen was discovered to be an individual substance by Cavendish in 1766, even though it had been in use for many years. The gas was given the name Hydrogen by Antoine Lavosier. The research of Antione Lavosier continued until he was unfortunately guillotined in 1794 during the French Revolution. The Judge of the time advised him that France had no need of scientists.
- Helium was first identified in 1868 by a French astronomer called Pierre Janssen whilst observing a solar eclipse. The new element was named Helium by Sir Edward Frankland and Sir Joseph Lockyer. In 1895 the gas was isolated by Rutherford.
- Argon was discovered in 1894 by Ramsey.
- Neon, Krypton, Xenon were all identified in 1898 by the teamwork of Ramsey and Travers.
Our Ecosphere.
Planet earth is covered with an atmosphere made up from a mixture of the above gases. We call this mixture air. Over the centuries we have dissected and divided our atmosphere into layers, and we have methodically given labels to all of these bits and bobs. We live in the bottom layer, sometimes called the boundary layer. This lower layer is part of the much bigger Troposphere, which extends upwards from sea level to a height of about 10,000km, stretching to perhaps 18,000km over the tropics. All of the worlds weather takes place in the Troposphere.
The boundary layer we live in is simply the interface between something moving and something that is relatively static. For example, if you poured dye into a river, you would see it moving smoothly with the river in some places, but down at the bottom of the riverbed it would be turbulent, due to the friction of the water as it flowed over the rocks and sand. The dye would swirl, causing patterns. This swirling occurs in the boundary layer, which is the layer where the water meets the sand.
The lower Troposphere is broadly the same. We have hot spots and cold spots, we have wet spots and we have dry spots. These all combine to produce various climatic conditions and weather changes, which can be compared to the dye swirling around on the river bed. In our living world, this turbulence produces clouds, rain, winds and storms.
Just like the dye at the bottom of our river, we can find a point of relative calm where things move smoothly. The technical name for things moving smoothly is called Laminar Flow, as opposed to Turbulent flow.
This apart, the atmospheric boundary layer that we live in is itself split into three separate layers. The bottom layer is called the 'roughness' layer with the symbol Z0.
When dealing with the 'thickness' of these layers another term is employed. The 'length'.
For clarity, the 'roughness length' is the thickness of the 'roughness layer'. The length of this layer will vary with the surrounding terrain. If the area is covered in buildings and skyscrapers, the roughness length will be greater than if the area is covered with miles of grass. The approximate calculation for Z0 is 1/30th of the average height of the surrounding terrain. If the area is covered with buildings with an average height of 60 metres, the roughness length = 2.
The term for the next length is the Surface Layer which has the term hs. This has a length (thickness) which typically from around 10 metres up to about 200 metres. Within this layer, the movement of air due to heat etc is assumed to be independent of height.
Finally, the upper part of the boundary layer is the Transition Layer which is also called the Elkman Layer. The transition layer extends from an altitude of hs to an altitude termed Zi, typically varying between 100 - 2000m.
The earth's atmosphere extends upwards to a height of about 50,000km, although you would be hard pressed to breathe at this altitude.
This means that most of our atmosphere is so high that it will be unaffected by the day to day turbulence on the planet surface below. Above our boundary layer, a semi-permanent airflow exists. These are sometimes called 'air pressure belts' and they are not affected by the day-to-day weather changes that we see. These air flows are dependant upon the movements of the sun, moon and stars, or any other slow change that we may wish to apply.